408 breaking up

Thanks for all the advice guys. To answer all the questions here are the specs right from the blue print site. also my carb is a Holley 4150 series race carb #hly-0-9379 in the summit catalog , my fuel system consists of a 1/2 " fuel line from the tank to a holley electric fuel pump then 1/2" line to a holley mechanical pump to a regulator(set to 6psi) then to the carb. The dyno sheet said 470 horse @ 5800 and 510 lbft torque @ 4100. I've always built my own motors but time was a factor and for a $500 difference I got a warranty and when its up theres room to make more power! I planned on checking all the basic easy stuff first but thought i'd pick everybodies brains before diving in.thanks again! Pete
Block:
Seasoned 360 block
Square and parallel decked
Align honed main bearing bore
Cylinders honed on computer controlled machine to within .0002 straightness and roundness
Cylinders are sonic tested for thickness

Rotating Assembly:
New SCAT cast iron crankshaft
Keith Black forged pistons
SCAT H-beam rods with 150,000 psi ARP bolts
Hastings Moly rings
Balanced rotating assembly
Melling high volume oil pump
Flat tappet hydraulic lifter camshaft
Heavy duty double roller timing set
Comp Cams Pro Magnum roller rockers

Cylinder Heads:
EDELBROCK Aluminum Performer RPM heads 1.437 diameter valve springs
Hardened retainers and springs
2.02 swirl polished intake valves
1.60 swirl polished exhaust valves
Hardened push rods
EDELBROCK RPM Air-Gap Intake
Mopar Performance polished aluminum valve covers
Brass freeze plugs
Dyno tested – and shipped with results
Critical Specs:
Camshaft:
.545 Int / .545 Exh & 241 Int / 2467Exh duration @ .050 - 110 degree lobe sep.
Compression Ratio:
10 to 1
Ignition Timing:
13 to 16 Degree Initial / 34 Degree Total

whew!
Thats better. I was hearing 280*-.480
so do you know what the jetting is?

make sure you actually have 6psi after the regulator, hope it's not a holley reg.